The present invention relates to rotary reactors for burning organic material which use inorganic particulate material to convey heat energy to the organic material to be burned and, more particularly, to assemblies for insulating the external recycle conduit of a rotary reactor.
A common device for incinerating hazardous materials and other toxic wastes is the rotary reactor. A rotary reactor includes a horizontally-oriented cylindrical drum or chamber which is rotated slowly about a horizontal axis concentric with the chamber by electric motors which engage ring gears mounted on the chamber.
The ends of the chamber are open and are received within annular hoods. The engagement includes a labyrinth seal which permits relative rotation between the chamber and the stationary hoods. At the inlet hood, fuel is injected into the chamber and burned to provide the heat for combusting waste, and other nozzles and orifices are provided to inject the waste material to be burned. Elongate lifters are mounted on the interior of the chamber and are oriented parallel to a central axis rotation of the chamber. Rotation of the chamber brings the lifters successively through a bed of inorganic particulate material, such as sand, located in the bottom of the chamber. As the lifters, loaded with sand, are rotated upwardly and above the sand bed, they gradually empty the sand downwardly back into the bed, thereby allowing the sand to be heated and intermingled with the waste materials to be burned. This action allows the sand to convey heat absorbed from the burning fuel to the waste material.
As the reactor chamber rotates, the inorganic particulate material progresses toward the end of the chamber opposite the fuel and waste inlets. In order to convey the particulate material back to the fuel and waste inlets, rotary reactors include a recycle conduit or chute. Such an apparatus is shown in Reed et al. U.S. Pat. No. 4,563,246. In one embodiment of that patent, the recycle chute comprises a helical conduit coiling about the outer periphery of the cylindrical chamber. The helical conduit communicates with the chamber at its front and rear ends and coils oppositely to the direction of rotation of the chamber. Particulate material entering the recycle conduit at the "downstream" end of the chamber flows to the "upstream" end adjacent the fuel and waste inlets by the rotation of the chamber.
Such recycle conduits typically are made of 253MA stainless steel which is appropriate for withstanding the high temperatures and corrosive environment within the chamber. However, this material rapidly radiates heat from the particulate material being conveyed to the upstream end of the chamber.
Accordingly, there is a need for insulating the recycle conduits of rotary reactors to minimize the heat loss from the particulate material recycled as it travels the length of the helical conduit. Conventional fiber insulating materials rapidly deteriorate as a result of the rotating action of the recycle conduit and the expansion and contraction of the conduit, predominately in a longitudinal direction, as a result of thermal stresses. Consequently, there is a need for insulating recycle conduits with a system that can accommodate the dimensional changes resulting from thermal expansion and contractions and which is not destroyed by the rotating movement of the conduit.